Invertebrate Zoology: A Study Guide - T. A. Dauda 2014

Multicellular Animals
Arthropods
Subphylum Tracheata - Class Insecta - Orders with Complete Metamorphosis - Order Diptera

The order Diptera comprises more than 85,000 species. Insects of this order possess a single (anterior) pair of membranous wings that are either transparent or pigmented. The posterior pair of wings is reduced, with their remnants modified into halteres. The mouthparts are piercing-sucking or sponging. Diptera are characterized by a mobile HEAD with large eyes and a robust Thorax, where the middle segment—to which the wings are attached—is the most developed. Diptera are the most agile fliers among insects. Their larvae are legless, headless, or possess an incomplete head.

The order Diptera is divided into 2 suborders: Nematocera (mosquitoes and crane flies) and Brachycera (flies).

Nematocera are characterized by long, multi-segmented antennae and an elongated abdomen. The larvae have a distinct head and biting mouthparts. This suborder includes various mosquitoes and mosquito-like insects, such as sand flies, biting midges, black flies, bloodworms, crane flies, and gall midges.

Mosquitoes have piercing-sucking mouthparts; males feed on floral nectar, while females feed on the Blood of warm-blooded animals. After a blood meal, egg maturation begins, followed by oviposition.

Mosquitoes lay their eggs in the Water of standing reservoirs, where the larvae develop. In the middle forest zone of Russia, 2–3 generations are typical, one of which overwinters.

Humans are attacked by mosquitoes of the genus Aedes, the common malaria mosquito, and occasionally by mosquitoes of the genus Culex (Fig. 78). The plumed midge is a harmless species.

Chironomids, or non-biting midges, can often be seen swarming in the air in a single spot on summer evenings. Chironomid larvae, frequently occurring in enormous numbers, inhabit the muddy bottoms of water bodies and constitute a vital food source for fish.

Sand flies are small insects up to 2.5 mm in length, closely related to mosquitoes. They are common in Crimea, the Caucasus, and Central Asia. Sand flies invade homes and deliver painful bites. Brachycera are characterized by short, usually three-segmented antennae, a broad and predominantly oval abdomen, and piercing or sponging mouthparts. Their larvae are either headless or possess a retractable head armed with hooks.

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Fig. 78 Representatives of the order Diptera:

1 — housefly; 2 — flesh fly; 3 — stable fly; 4 — bluebottle fly; 5 — malaria mosquito; 6 — Culex mosquito.

The head of the common housefly bears two large eyes covering almost the entire head, allowing the fly to see in all directions. Houseflies also possess a remarkably keen SENSE OF SMELL, enabling them to home in on odors with great speed. The ability of flies to adhere to and walk on walls or ceilings is due to the presence of a pair of "adhesive pads" on their tarsi, alongside claws, which are kept constantly moist by secreted fluid.

In indoor environments, alongside the housefly, the lesser housefly and the attic fly are common. All of these insects deposit their eggs in decaying matter (such as refuse dumps and landfills), manure, and human excrement, thereby acting as vectors for the PATHOGENS OF INTESTINAL infections and helminth eggs. Bacterial infection is transmitted via the sponging labellum and the adhesive pads on the tarsi. Furthermore, pathogenic Bacteria typically pass through the fly's gut undigested and are deposited onto food via its excrement.

It is often said that in autumn flies become aggressive and inflict painful bites. However, none of the aforementioned flies sting. In late summer and early autumn, the stable fly frequently enters houses. It features a rigid proboscis equipped with piercing bristles, allowing it to pierce Skin and feed on blood, primarily attacking domestic animals.

Human dwellings are also frequently visited by large bluebottle flies, flesh flies, and smaller green bottle flies (up to 3 mm in length).

Among flies, there are species that damage agricultural crops, such as the cabbage ROOT fly, whose larvae feed on cabbage roots, and various frit flies that harm cereal grains.

Females of large horseflies are blood-feeders that severely distress livestock (horses, cattle) and can transmit a range of diseases.

The larvae of certain flies, particularly botflies, parasitize the skin of various animals, causing intense itching and tissue damage. Nevertheless, among flies with parasitic larvae, There are also beneficial species, such as tachinid flies. Their females deposit eggs or larvae directly into the bodies of other insects, including harmful caterpillars. Consequently, tachinids are utilized in biological pest control.

In summer, hoverflies commonly fly around and alight upon flowers. Many of them mimic bees, wasps, and bumblebees in shape and coloration. While some hoverflies are agricultural pests, such as the onion hoverfly, others are beneficial to humans. For instance, syrphid larvae inhabit plant leaves and feed on aphids.

Phylogeny of the Phylum Arthropoda

The Origin of the phylum Arthropoda is broadly understood. Their ancestors were primitive, homonomously segmented Annelids belonging to the Class Polychaeta. The transition from annelids to Arthropods was accompanied by progressive structural complexification: the Transformation of a relatively thin cuticle into a rigid exoskeleton, the subdivision of the integumentary-muscular sac into discrete Muscles, The Emergence of a mixocoel (hemocoel), the modification of parapodia into jointed appendages, the Differentiation of the dorsal vessel into a more distinct Heart, The Development of compound eyes, as well as the gradual replacement of homonomous body segmentation with heteronomous segmentation and The process of cephalization—namely, the incorporation of anterior trunk segments into the head and the transformation of their appendages into mouthparts.

Certain arthropods retained the ancestral aquatic lifestyle of annelids, along with their aquatic respiratory Organs, specifically external cutaneous gills. Given that the gills of polychaetes were located on the parapodia, they retained the same position in lower representatives of the phylum Arthropoda, with the distinction that the parapodia became articulated and transformed into true limbs. The palps of ancestral forms presumably gave rise to the antennules of arthropods.

Among the most primitive arthropods are trilobites (subphylum Trilobitomorpha). These ancient Paleozoic animals differ markedly from the representatives of another group that also retained A number of primitive ancestral traits—the subphylum Crustacea (Branchiata). Trilobitomorpha persisted until the end of the Paleozoic, leaving behind modified descendants known as Chelicerata. The latter lost their antennules; their first pair of head appendages differentiated into chela-bearing chelicerae, the second into pedipalps, and the remaining two pairs transformed into the first two pairs of walking legs. Similar to the walking legs, the appendages of the two anterior trunk segments also differentiated; in most chelicerates, these fused with the head to form a cephalothorax, while the remaining segments formed the prosoma and opisthosoma. Thus, Chelicerata are linked to Polychaeta via trilobites. The lower classes of chelicerates, much like their ancestors, are aquatic animals utilizing branchial Respiration, whereas the highest class—Arachnida—adapted to a terrestrial existence.

The other branch, as previously mentioned, is represented by branchiate arthropods (subphylum Branchiata). Their four anterior segments become incorporated into the head, and their respective appendages give rise to antennae and three pairs of jaws. Nonetheless, cephalization in many crustaceans remains at a relatively primitive level.

The subphylum Tracheata constitutes yet another group of arthropods closely related to the subphylum Branchiata, with which they share numerous characteristics despite their terrestrial mode of life.

Since the annelid ancestors of the phylum Arthropoda possessed an indefinitely large number of homonomous segments, it is natural that this structural feature is also characteristic of the most primitive arthropods. Tracing the evolution of individual Branches of the phylum Arthropoda, we observe a number of parallel processes. Thus, across all arthropod lineages, we consistently see a gradual decrease in the number of segments, i.e., oligomerization takes place. Concurrently, the heteronomy of segmentation increases, accompanied by the differentiation of the segments themselves, the appendages, and the initially metameric Internal Organs. Other changes are attributed to a common origin. In diverging branches, however, the transition to a similar lifestyle leads to analogous adaptations (the emergence of tracheae, the development of Malpighian tubules, etc.).

QUESTIONS FOR SELF-check and review:

1. What are the habitats of myriapods?

2. What is the External Structure of myriapods?

3. What are the distinctive features of millipedes, soil centipedes, stone centipedes, and the banded centipede?

4. What habitats do insects occupy in relation to their morphological diversity?

5. What is the external structure of insects?

6. What role do body integuments play in the life of insects?

7. What is The structure of the internal Organ Systems in insects, and what advantages do these provide to the animals?

8. What types of development are distinguished in insects?

9. What organizational and behavioral features characterize the representatives of orders with incomplete metamorphosis: mayflies, dragonflies, cockroaches, orthopterans, lice, and true bugs; and with complete metamorphosis: beetles, caddisflies, butterflies and moths, Hymenoptera, fleas, and flies?